Are you talking about just the kernel or the entire system ??
If just the kernel, don't worry, by default RHEL keeps a few old kernels when installing new ones.
If you're talking the whole system, then restore from backup. But there's almost no chance that something that works on 5.x won't work on 5.y.
Last edited by AlucardZero; 11-15-2011 at 08:22 AM.